The deep frying of foods in oil such as for example fish and chips has long been practiced on a commercial basis. The equipment used is generally in the form of large volume stainless steel tanks, frequently gas fired. Commonly the heating source or sources are so arranged as to maximize the useful life of the large volumes of expensive cooking oil by minimizing the harmful carbonizing of the oil. Such carbonizing is caused by high concentrations of heat per unit area at the heating source.
It is usual also in such commercial systems to incorporated a cool area at the base of the tank which allows any carbonized particles which may form to collect in this cool area and thus be isolated from further heating. This is an important consideration in the design of deep frying equipment since some studies have linked carbonized heating oil to detrimental health effects.
In recent years the market has seen the development of a range of electric deep frying appliances, primarily intended for domestic use. They generally fall into two categories: bowls with separate heating elements depending into the bowl and bowls with fixed external heating elements. Both categories suffer from a number of disadvantages.
In the interest of cleaning, the elements and electrical control unit of deep fryers in the first category, are generally removable as a unit. The heating elements of these units generally employ a tubular heating coil bent into some suitable pattern to distribute heat to the oil in which the element is immersed. Because the length of such tubular coils is limited by practical restrictions inherent in their manufacture, the resulting ratio of heat energy emitted per unit area to achieve a required deep frying temperature is very high; sufficiently high to induce carbonizing.
Another difficulty in this first category of deep frying appliances is the positioning of the thermostat thermocouple. It is necessary to control not only the cooking oil temperature prior to the addition of cold food, but also to quickly sense the temperature reduction as a result of the addition of such food. If the temperature controlling device does not sense a reduction in oil temperature quickly enough and re-energises the heating element, the food will absorb excessive amounts of oil. To compensate for this lag in thermal response, many deep fryers have higher than desirable initial oil temperature settings, which results in the inevitable rapid degradation of the oil.
Additionally, because of the danger of igniting cooking oil, regulatory authorities subject deep fryers to rigorous testing. It is a requirement of sale, for example, that if a deep fryer is turned on with either no oil, or only a remaining oil residue after emptying, that no fire will be ignited. The thermocouple must react both to the oil when present, and the heating element when no oil is present.
A known solution has been to attach the thermocouples and their connection tubes to the coils but this renders them vulnerable and makes cleaning difficult.
In deep frying appliances of the second category, the heating element is often attached to the underside of the bowl. This inevitably leads to considerable inefficiency as only a proportion of the heat emitted by the element can be transferred to the oil inside the bowl. Again the configuration of the heating element is generally that of a single coil so that the heat induced per unit of surface area of the bowl is likely to be considerably higher than desirable. This second category of fryers has traditionally used thermostats attached to the outside of the heating bowl. As a result, it is difficult for these to quickly sense a drop in internal oil temperature, and thus cooking performance suffers.
Additionally, carbonised materials gravitate to the hottest part of the container and degrade the oil rapidly
It is an object of the present invention to address or ameliorate at least some of the above disadvantages.